Method for desulfurizing molten metal and in particular liquid pig iron



Sept. 29, 1959 M. ALLARD :TAL 2,906,616

METHOD FOR DESULFURIZING MOLTENMETAL AND IN PARTICULAR LIQUID PIG IRONFiled Feb. 21, 195s United States Patelfrt NITHOD FOR DESULEURIZENGMOLTEN METAL AND IN PARTICULAR LIQUID PIG IRON Marc Allard, BernardTrentini, and Lucien Wahl, Saint- Ggermain-en-Laye, France, assignors toInstitut de Recherches de la Siderurgie, Saiut-Germain-en-Laye, France,a professional institution ofFrance Application February 21, 1956,Serial No. 567,032

Claims priority, application France April 28, 1955 13 Claims. (Cl. 75-51) Our invention has for its object a new method for desulfurizingmolten metal and in particular liquid pig lron.

Even small amounts of sulfur have an extremely high objectionable effecton the grade of cast iron and steel and consequently it is generallydesired to remove the sulfur through various means during the productionof liquid pig iron or steel.

For instance, `it is possible to charge the blast furnace with langeamounts of limestone or manganese ore so as to obtain operation underhighly basic conditions or else to produce high manganese hot metal, butsuch procedures are. expensive by reason of the increased consumption offuel thus required or of the cost of manganese ore. It is also possibleto remove the sulfur from the steel in the electric or open-hearthfurnace through the agency of highly basic slags but such methods aregenerally expensive and reduce the yield of the furnaces.

It has been proposed since a long time to resort to methods forVdesulfurizing liquid pig iron outside the actual producing apparatusand generally sodium carbonate is resorted to for this purpose and thissodium carbonate admixed with the liquid pig iron inside a ladle allowsremoving a part of the sulfur, but it shows however the drawback ofleading to the production of a highly fluid corrosive slag together withthe release of noxious vapors. Furthermore, said prior method does notallow obtaining very low sulfur contents or removing the large amountsof sulfur contained in the liquid pig iron produced through certainmethods such as the acid operation of the blast furnaces or again whenusing certain ores or certain cokes.

On the other hand, solid lime the desulfurizing properties of which arewell known does not show the above mentioned drawbacks and has oftenbeen resorted to for desulfurizing the liquid pig iron.

Thus, it has already been attempted to desulfurize liquid pig iron,through the agency of crushed burnt lime to which is incorporatedpulverulent coke, inside a rotating furnace heated with gases producedin a coke oven or else with atomized coal. In spite of operative cycleslasting several hours it has not been possible to reach inthis mannerVery small residual contents of sulfur.

Similarly, a method is known which allows treating with the best resultsliquid pig iron, inside a cylindrical container revolving at a highspeed, through the agency of pulverulent lime to which is possiblyincorporated pulverulent coke and which is introduced before thebeginning of operation over the metal bath, while the introduction ofoxidizing substances before and after operation is limited to an amountas small as possible.

A further method is known according to which the lime admixed withlluorspar is fed into the metal bath and is stirred through the agencyof a low frequency alternating current.

All the above mentioned prior methods show various advantages anddrawbacks and lead to more or less satisconcerns industrial operation,more particularly Whenit is,y necessary to take into account a highrhythm of production,

Suclrmethods do not :resort furthermore to any suspension'of lime in astream'of gas.

However, in the. case of oxidizing and deoxidizing reactions, methodsexist which provide for the suspension vof ulgerulent material in a gasand its blowing intoV a metal As concerns vdesulfurizing reactions,methods are also known according to which the desulfurizingy reagent issuspended inside a stream of gas and theninjected by means of a lanceinto kthe metal bath contained in a crucible or in a ladle or in anelectric furnace. Those methods which resort to lime as a desulfurizingreagent in association with-.a non oxidizing gas such as nitrogen forinstance, although they may lead to a substantial removal.v of sulfurhave however not allowed obtaining systematically a high rate ofdesulfurization leading to low final contents of sulfur in the treatedliquid pig iron and this comparative. failure explains Why the injectionof y pulverulent lime through a lance has not been developed onanwindustrial scale for the execution of high desul furizing procedures.

metal.

deep immersion of the lance forms a serious problem.

Even if this problem is solved for conventional indus-v trialoperations, there remains an important reason for the failure of priorattempts towards reaching systemati cally low contents of sulfur, saidreason residing in the: actual nature of the method for blowing the limethrough; the immersed lance which leads to a local action of the blowndesulfurizing reagent so that if locally and round the lance large ratesof sulfur removal are obtained, the: remainder of the bath is notreached at once by the reagent and is onlyv reached partly andsubsequently; This drawback is all the more serious for a given durationof treatment when the mass of metal to be desulfurized during a singleoperation is higher and this will be readily understood .since the massof desulfurized metal round the lance corresponds to only a smallfraction of the mass to be =desulfurized so that the result is a loweraverage rate of sulfur removal.

Our invention which is the result of numerous experiences made byourselves both on a pilot scale and factory results, but none iscompletely satisfactory as on au industrial scale has for its object anindustrial sulfur-removing method which shows none of the abovereferred-to drawbacks by reason of its resorting to a combination ofsteps leading to a very energetic, rapid and economical elimination ofsulfur out of molten metal and in particular out of liquid pig iron.

A further object consists in removing large amounts of sulfur containedin the cast iron produced through acid methods in blast furnaces or thelike apparatuses.

A still further object of our invention consists in obtaining within. avery short duration very low contents of residual sulfur in such liquidpig irons, which contents may be in fact not measurable throughconventional chemical analyzing methods, a result which is verydifficult or in fact impossible to reach through any other knownmethods.

A systematic series of investigations relating to the transformation ofthe sulfur in a basic Bessemerl con-v verter has conrmed the existence,already mentioned by' prior experirnenters, of a certain grade of sulfurremoval, often of the magnitude of 15 to 20% appearing at the beginningof the rening of liquid pig iron in a basic Bessemer converter. Thisdesulfurization produced by the stirring of the liquid pig iron withlumps of lime incorporated into the charge at the beginning of operationis speedily brought to an end, chiey as a oonsequence of the oxidationof the silicon through the oxygen of the air blown into the converterduring the refining.

Comparison with the particular problem of the removal of sulfur out ofliquid pig iron has allowed us to foresee that, provided the air isreplaced by a nonoxidizing gas while the lumps of lime introduced at thebeginning of the operation are replaced by pulverulent lime blown withsaid gas through the blow holes, the advantages of the intimate Contactand intense stirring obtained in a converter through said blowing wouldallow obtaining a substantial and speedy desulfurizing of the liquid pigiron. In order to obtain a very high desulfurization ratio,desulfurizing executed by means of lime requires non oxidizingconditions, which is a wellknown fact ascribable to the general laws ofthermo dynamics (in particular Le Chteliers law).

Tests executed on a pilot scale have brought a complete conrmation forthese assumptions, to a point such that the results were rapidly appliedon an industrial scale.

The efficiency and speed of desulfurizing are due to the blowing intothe converter of lime powder together with a non-oxidizing or veryslightly oxidizing gas, as provided through the agency of tuyeresopening into the wall or the bottom of the apparatus and which lieunderneath the metal level during operation, which leads to stirringunder intimate contacting conditions the desulfurizing substance withthe metal to be desulfurized, and this is all the more true because theactual movement of the bath may be associated with a relative movementof the tuyeres. In the case for instance of the application of aconverter to such a desulfurizing operation, the tilting of theconverter round its axis through a predetermined angle will constraineach tuyere to sweep through the same angle.

The high speed of the operation is of particular advantage for thelimitation of loss of heat, which is of a considerable interest foroperations on industrial scale, said advantage being increased when thecontainer serving for the transportation of the metal serves also fordesulfurizing purposes, since it is possible to prevent thus any drop intemperature arising as a consequence of the transfer of the metal fromone container into another.

Our improved method distinguishes clearly from the known methods forblowing pulverulent lime suspended in a stream of gas through the agencyof an immersed lance because the stirring and contacting conditionsobtained when blowing through tuyeres covered by the molten metal duringoperation with the sole object of desulfurizing the metal are far betterand allow desulfurizing the latter to a very marked extent in a Veryspeedy manner Whereas the use of an independent immersed lance does notallow obtaining, chiey in the case of industrial operation, anequivalent desulfurization within so short a time with the sameconsumption of the same desulfurizing substance.

Our method distinguishes also fundamentally from the numerous methodsusing the blowing of various powdery products in order to obtain in asame vessel severai metallurgical operations such as desulfurization,desiliconization, dephosphorization. As previously stated, in order toobtain a rapid and important desulfurization, it is fundamental that thevessel be used for dcsulfurization only.

Our invention will be now described in a more specic accompanyingdrawing the single figure of which is a. diagrammatic showing of a plantintended for the execution of our invention inside a converter as acontainer for the reaction media.

As illustrated, the plant includes chiey an apparatus 1 in the shape ofa steelwork converter the capacity of which is of the order of 300kilograms of metal to be treated, said converter being adapted to betilted round its axis 2 through the agency of an electric motor which isnot illustrated, the plant including further a powderdistributor 3designed in a known manner and feeding uniform outputs of highlyconcentrated suspensions of a very tine powder, a group of bottles 4containing cornpressed nitrogen, a pipe 5 feeding the nitrogen with thesubsequent admixture of the desulfurizing reagent to the tuyeres 6extending through the bottom of the small converter and lastly a controlboard 7 for checking and adjusting operation.

This control board shown very diagrammatically at 7 carries themanometers, the tlowmeters and the dierent valves through which it ispossible to control and adjust the tlow of the fluid carrying theoperative powder. We have illustrated in the drawing the uid conveyingchannels 8 connecting the valves and measuring instruments on thecontrol board with the corresponding elements of the blowing system. Wehave shown at 9 the scale which allows adjusting as required the openingof the powder distributor device. Lastly we have illustrated at 10 thepressure reducing and measuring valve for the battery of gas-containingbottles of which only two have been illustrated at 4 on the drawing.

To the refractory wall 11 of the converter is secured the converterbottom at 12 provided with tuyeres 6 forming tubular connections withthreaded outer ends 13, which ends carry through the agency of fasteningcollars 14 the lime distributing tubes 15. The substances to beprojected into the converter are fed through a yielding pipe 16connected with the tube 5 at one end and through the threaded connection17 at the other end with the lime distributing tubes 15. It should beremarked that the blowing means do not include any Wind box.

Many other types of apparatuses may be used for executiug our invention.Thus, instead of a converter, we may resort to a tilting ladle whichserves both for the transportation of liquid pig iron and for theexecution of the desulfurizing operation. During the transportation ofthe liquid pig iron, the tuyeres in the ladle project above Ithe levelof the molten metal so that they may be brought through a tiltingmovement of the ladle round its axis underneath the level of the bathduring the desulfurizing operation.

It is also possible to resort to a special intermediate containersimilar to a so-called tea-pot ladle and to subject the liquid pig ironto a continuous treatment during the casting of the blast furnace.

The method according to our invention which may be executed in thearrangement referred to hereinabove, consists in producing a suspension,inside a neutral or slightly oxidizing or reducing gas of thedesulfurizing agent in the form of a highly subdivided powder, saidsuspension being very concentrated so as to damp the cooling action ofthe carriergas and to reduce the duration of the operation; thesuspension formed is then blown into the metal bath through the openingsprovided in the bottom or along the wall of the metallurgical containercarrying the molten metal to be treated, said openings registering withthe inside of the bath underneath the level of the latter in thecontainer.

The desulfurizing agent used should be of a very tine granulometry suchfor instance that it may pass entirely through a 20 mesh Tyler sieve. Itis possible to use advantageously pulverulent lime or more generally anoxide or a compound of alkaline or earth alkaline metal or magnesia or amixture of such oxides or compounds.

1t is also possible to resort to one or more of.the precedinglymentioned desulfurizing agents with' theaddition of pulverulent reducingsubstances.

The desulfurizing agent may also act as a reducer in -which case it isconstituted eg. by calcium carbide. or calcium cyanamde.

As to the carrier gas it is also possible to use variou gases for thispurpose. Although we prefer using nitrogen, it is possible toincorporate into the carrier gasa reducing gas such for instance ashydrogen or. carbon monoxide or hydrocarbons.

The following examples are given by no means ina limiting sense but onlyto show various means f'orfexecuting our invention together with theresults which may be expected. v

p Example 1.-A small converter provided with .abasic lining andltuye'res associated, therewith is heated up to 1000" C. and laidhorizontally. A ladle containing about 300 kgs. of liquid pig ironpreviously meltedin a small induction furnace is then brought nearthefconverter so that themetal may be poured into thelatter.

Immediately after the liquid pig. iron has beenv poured into the.converter, a sample is removed and shows sulfur contents of 0.080%,thetemperature of ltheliquid pig iron being equal to 1300" C. Thenitrogen is .then.intro duced and a few seconds afterwards, the powderdis.- tributor is adjusted so as to produce the desired flow. Thedesulfurizing agent used in said example. isV constituted by crushedcommercial burnt limeadapted. to pass through a mesh Tyler sieve. It isa well known fact that lime when crushed assumes for its major part theform of a flour dust. The appearance of a White cloud'at the mouth ofthe converter is a signal meaning that the converter is then to beraised into its vertical position. The blowing is then performednormally without any substantial projection out of the converter. Allame appears at the mouth of the converter and this ame shrinksgradually during the operation togethervr with the small cloudof lime;in the case considered the output of lime is equal to ahout3 kgs. perminute. After the blowing has lasted about 3 minutes, the converter isreturned into its horizontal position while its lime and nitrogencircuits are cut off in succession. A sample removed 20 seconds afterthe converter has been returned into its horizontal position showssulfur contents of 0.006%, which corresponds to-a rate ofdesulfurization equal to 93%. The metalvbathi's then poured without anydifliculty into a ladle while the desulfurizing mixture remains insidethe converterv and may be removed for its major part through a completetilting down of the converter.

The following Table I gives further details relating tothe above test inparticular as concernsthe composition of the liquid pig iron.

We may also mention .in said Table I the data relating to two othertests made on about 300 kgs. of metal with commercial lime of the samebatch as in the preceding test tof which other tests that numbered 3relates in particular-to the treatment of liquid pig iron with highcontents of sulfur equal to 0.191%

The use of only 300 kgs. of metal for successive tests whichareseparated from one another by-substantial intervals :of several hoursis somewhat objectionable, and leads to a consumption of lime which ishigher than that required in the case of continuous operation or whenvtreating larger amounts of metal during `a single teSt.

Example 2.-It has been found in fact through tests ont'larger amounts ofliquid pig iron inside av converter of 2.5 to -3 Itons that thediiculties encountered have been smaller.

The above Table I also shows the result of foury tests made on a largerscale while resorting to commercial lime ofthe same type as inthepreceding eXample:-two of' these tests included a blowing period of 3minutes and.the two others a blowing period of only l minute and" 30seconds. The consumptions of lime were of a magnitude ofA 2% of theweight of treated metal while the rate of desulfurization ranged between83 and 94%. The concentrations of lime in the nitrogen are very high andreach 40 kgs. per cubic meter. In allthe cases the samples have beenremoved immediately after the apparatus has-been titlted down withoutwaiting for any settling as is generally required with other knownblowing methods. The rhythm of production is very high since the pouringinto a ladle of the treated iron may be executed as soon as the blowingof the pulverulent lime through the bath is at an end.

Example 3.-The speed and; the4 eiciency of the desulfurizing methodresorting to pulverulent lime according toour invention are evidenced ina particularly clear manner by the following testexecuted with anapparatus containingl 2,500 kgs. of metal as shown in the followingTable II. In said test less than Sminutes after the beginning of theoperation, the liquid pig iron is practically devoid of any sulfur.

Tab le II Weights of Duration Weight Desulfur- Sample metal in ofblowing of lime Percentage ization ef- No. kg. in minutes in kg. ofsulfur eiency, percent 1 Starting value.

Example 4.-We should also mention the' use of lime Table I s at the s atthe gli/ig: Weight of Duration Weight C, Mn, l Si, P, beginning end ofthe tion Test No. metal in of blowing of lime percent percent percentpercent of the operation, effb kg. in minutes in kg. operation, percentciency l percent percent 1Desulfurization efficiency is defined by:

S, at beginning -S, at end S, at beginning with the addition ofpulverulent charcoal; the Table lII refers to tests executed with amixture of of lime with 20% of charcoal.

Example 5.-We should further mention the use of lime of the same type asprecedingly with the addition of a small percentage of pulveruleiitaluminium; in Table 'IV are recorded the data corresponding to testsexecuted in apparatuses containing 300 and 2500 kgs. of metal with apercentage of aluminium equal to 2% of the Weight of lime.

The efficiency of the method is such that very small amounts ofmagnesium are suicient for the substantially complete elimination of thesulfur out of the liquid pig iron .to be treated and it will be readilyunderstood that the method is of a considerable economical interest inparticular when applied to certain problems such as that of nodular castiron.

Example 8.-It is possible to substitute for the lime, according to thelocal conditions or present problems, oxides or compounds of alkaline orearth alkaline metals or mixtures thereof or else magnesia or burneddolomite, any of said oxides or compounds or mixtures thereof beingblown into the cast iron in accordance with our improved method. The useof magnesia or burned dolomite in particular can be of advantage lforthe treatment of liquid pig iron at high temperature since the meltingpoint of the slag forming in the presence of silica and iron oxide israised through the presence of Table l V v magnesia and thus thedesulfurization may be continued We. ht iD t W ht S S Desuuur untilminimum contents are actually obtained.

l 0 1.1181011 @l Test nietgal in of blowof liue at the at the izationExample 9 may 315.0 resort Q other desulfuflzlflg N0. kg. ing in in kg.stamt Gnd Dremmene?, agents such as calcium carbide or calcium cyanamidewith mmutes pern ce perce yields which are far better than with themethods applied hitherto, this being ascribable to the large contacting300 3' 7 0.059 0. 006 92 r 300 31 7. 5 0.058 0003 95 25 surfacesprovided by the use of tuyeies opening into 2 ggg f 30 g ggg; gg thebath. Table VII shows the results obtained with 2; 500 3f 72 0j000 0100403 three tests executed respectively with calcium cyanamide 2,000 3 690-136 0- 010 93 admixed with aluminium with lime incorporating calciumcarbide and with lime incorporating calcium cyanamide.

Table VII Blown Dura- Sulfur contents at Contents of carbon and silicon,at- Temperweight tion of ature ot' Test Blown mixture in perblowtheliquid N o. cent of ing in Start, pig iron metal niinpercent End,percent Start End at start,

bath utes O.

Lime plus 20% calcium carbide. 3 0.0 3.840 and 0.07Si... 3.780 and0.52Si. 1,375 Lime plus CNgCa 3 3 0.071 3.750 and 0.58Si.. 1.355 CNgCaplus 2% A1 3 o. 053 3.650 and 0.69Si..- 3.630 and 0.49Si.. 1.380

Example 6.--We will give further details relating to the test Number 3shown in the Table IV so as to emphasize the extraordinary speed andeiciency of the method even in the case of liquid pig iron with highcontents of sulfur, say 0.3% in the test Number 3 referred to.

Table V Weight of Duration Weight of Desuliur- Number of metal in oblowlime in Sulfur in ization efsarnple kg. ing in lig. percent feiency,minutes percent Example 7.--We may also mention the use of lime intowhich is incorporated a small percentage of pulverulent magnesium; theTable VI shows two tests executed respectively on 300 kgs. of liquid pigiron with lime incorporating 2% of magnesium and on 2,500 kgs. of liquidpig iron with lime containing only 1% of magnesium.

Subsequent tests have allowed a substantial reduction of the consumptionof carbide or cyanamide, which is somewhat large in the case of thesefirst tests.

Example .70.-A further embodiment of our invention consists in resortingto a carrier iluid constituted by a gas which is itself an energeticreducing agent. It might be preferable not to use pure hydrogen for thispurpose by reason of the dangers arising in the handling of this gas andwe have executed a test with a suspension of lime in nitrogen with theadmixture in the latter of a small amount of ammonia. Thedesulfurization obtained is particularly large in this case as shown inTable VIII. Obviously it is also possible to use hydrogen, provided theplant is designed specially for the use of such a gas.

But it is also possible in accordance with local conditions to resort.to other gases, such for instance as coke oven gases or natural gases.

Obviously the above disclosed examples and the diagrammatic showing ofthe arrangement used have been given solely by way of examples and by nomeans in a limiting sense and the methods may be executed in any otherdesired manner within the scope of the accompanying claims.

What we claim is:

1. In a method of desulfurizing molten metal with a selecteddesulfurizing agent, the step of introducing into a bath of molten metalin liquid state a highly concentrated suspension containing at leastkgs. of finely subdivided particles of said selected desulfurizing agentper cubic meter of gas so as to speeddue to said high concentration ofsaid linely subdivided solid particles of desulfurizing agent in saidrelatively small quantity of gas -the rate of reaction to such a valuethat the temperature drop of the molten metal-due to admission of saidgas--is so small that the desulfurizing reaction takes place at a hightemperature and before a considerable temperature drop occurs, therebyensuring reaction between said molten metal and said selecteddesulfurizing agent at a temperature at which the efficiency of thedesulfurizing action of said selected agent is substantially greaterthan after said considerable drop of the temperature of the moltenmetal.

2. In a method of desulfurizing molten metal with a selecteddesulfurizing agent, the step of introducing into `a bath of moltenmetal in liquid state a highly concentrated suspension containing atleast 5 kgs. of finely subdivided particles of said selecteddesulfurizing agent per cubic meter of gas and at a high speciiicadmission rate equal to at least 19 kgs. of said desulfurizing agent foreach 3,000 kgs. of molten metal per minute, so as to speed-due to saidhigh concentration of said finely subdivided solid particles ofdesulfurizing agent in said relatively small quantity of gas and due tosaid high specific admission rate-the rate of reaction to such a valuethat the temperature drop of the molten metal-due to admission of saidgas and due to the time needed for such admission-is so small that thedesulfurizing reaction takes place at a high temperature and before aconsiderable temperature drop occurs, thereby ensuring reaction betweensaid molten metal and said selected desulfurizing agent at a temperatureat which the efiiciency of the desulfurizing action of said selectedagent is substantially greater than after said considerable drop of thetemperature of the molten metal.

3. A method of desulfurizing molten metal as defined in claim 1, whereinsaid selected desulfurizing agent is introduced simultaneously at aplurality of points spaced from each other and located below the uppersurface of said bath of liquid metal.

4. A method of desulfurizing molten metal as defined in claim l, whereinsaid selected desulfurizing agent is introduced simultaneously at aplurality of points located spaced from each other at the bottom of saidbath of liquid metal.

5. A method of desulfurizing molten metal as defined in claim l, inwhich said molten metal is a molten ferrous metal in liquid state.

6. A method of desulfurizing molten metal as defined in claim 1, inwhich said molten metal is molten pig iron in liquid state.

7. A method of desulfurizing molten metal in liquid state as defined inclaim l, wherein said finely subdivided particles of said selecteddesulfurizing agent are capable of passing through a 20-mesh Tylersieve.

8. A method of desulfurizing molten metal in liquid state as defined inclaim l, wherein the concentration of said finely subdivided particlesof said selected desulfurizing agent in said gas is between about 5 kgs.and about 40 kgs. of said particles per cubic meter of said gas.

9. A method of desulfurizing molten metal in liquid state as defined inclaim l, wherein said selected desulfurizing agent is pulverulent lime.

10. A method of desulfurizing molten metal in liquid state as defined inclaim l, wherein said selected desulfurizing agent is selected from thegroup consisting of lime, oxides of alkaline earth metals, calcineddolomite, calcium carbide and calcium cyanamide.

ll. A method of desulfurizing molten metal in liquid state as defined inclaim l, wherein, together with said selected desulfurizing agent, arelatively small quantity of a pulverulent reducing substance isintroduced into said bath of molten metal.

12. A method of desulfurizing molten metal as defined in claim l,wherein, together with said selected desulfurizing agent, a relativelysmall quantity of a pulverulent reducing substance selected from thegroup consisting of carbon, aluminum, magnesium, calcium carbide andcalcium cyanamide is introduced into said bath of liquid metal.

13. A method of desulfurizing molten metal in liquid state as defined inclaim l2, wherein said selected desulfurizing agent is lime and saidreducing substance is aluminum.

References Cited in the file of this patent UNITED STATES PATENTS239,621 Pirath Apr. 5, 1881 387,952 Fronheiser Aug. 14, 1888 1,043,371Sundberg Nov. 5, 1912 1,471,401 Koppers Oct. 23, 1923 1,590,730 Evans.lune 29, 1926 2,290,961 Heuer July 28, 1942 2,502,259 Hulme Mar. 28,1950 2,577,764 Hulme Dec. 11, 1951 2,587,573 Wynne Feb. 26, 19522,665,982 Crego et al. Jan. 12, 1954 2,692,196 Hulme OCt. 19, 1954FOREIGN PATENTS 622,419 Great Britain May 2, 1949 OTHER REFERENCES Campand Francis: The Making, Shaping and Treating of Steel, 6th edition, pp.385486, section III, Operation of the Plant, U. S. Steel Co.,Pittsburgh, Pa.

1. IN A METHOD OF DESULFURIZING MOLTEN METAL WITH A SELECTEDDESULFURIZING AGENT, THE STEP OF INTRODUCING INTO A BATH OF MOLTEN METALIN LIQUID STATE HIGHLY CONCENTRATED SUSPENSION CONTAINING AT LEAST 5KGS. OF FINELY SUBDIVIDED PARTILCES OF SAID SELECTED DESULFURIZING AGENTPER CUBIC METER OF GAS SO AS TO SPEED-DUE TO SAID HIGH CONCENTRATION OFSAID FINELY SUBDIVIDED SOLID PARTICLES OF DESULFURIZING AGENT IN SAIDRELATIVELY SMALL QUANTITY OF GAS THE RATE OF REACTION TO SUCH A VALUETHAT THE TEMPERATURE DROP OF THE MOLTEN METAL-DUE TO ADMISSION OF SAIDGAS-IS SO SMALL THAT THE DESULFURIZING REACTION TAKES PLACE AT A HIGHTEMPERATURE AND BEFORE A CONSIDERABLE TEMPERATURE DROP OCCURS, THEREBYENSURING REACTION BETWEEN SAID MOLTEN METAL AND SAID SELECTEDDESULFURIZING AGENT AT A TEMPERATURE AT WHICH THE EFFCIENCY OF THEDESULFURIZING ACTION OF SAID SELECTED AGENT IS SUBSTANTIALLY GREATERTHAN AFTER SAID CONSIDERABLE DROP OF THE TEMPERATURE OF THE MOLTENMETAL.